Pneumatic thermostat

ABSTRACT

An improved pneumatic thermostat is provided which is capable of generating from a variable pressure air supply a pressurized air signal indicative of ambient temperature. The thermostat is used in conjunction with an air flow regulator in an air distribution system and utilizes as an air supply a portion of the air flow being distributed. The thermostat utilizes a pressure reducing valve which is referenced to pressure downstream from the air flow regulator, a flapper and nozzle pneumatic mechanism activated by a bi-metallic lever, and a self-aspirating arrangement which insures the bi-metallic lever is continuously sensing the true ambient temperature.

This is a continuation-in-part of copending application Ser. No. 472,337filed May 22, 1974 now abandoned.

BACKGROUND OF THE INVENTION

The present invention relates generally to apparatus responsive totemperature and, more specifically, to an improved pneumatic thermostatto be used in conjunction with air flow distribution systems.

Systems for automatically controlling the environmental temperature inhabitable, enclosed areas generally employ a fan pressurized air sourcewhich supplies air through ducts to the various rooms or portions of theenclosure. In each room one or more terminal ports may be found whichtypically employ ceiling-mounted diffusers in order to direct thedischarged air horizontally along the ceiling. If pressure increases inthe duct system causing the flow through the diffusers to becomeexcessively high objectionable velocity noise may result. On the otherhand, if the flow becomes excessively low, the air does not movehorizontally along the ceiling when discharged from the diffuser, butrather drops directly down causing what is known as cold air dumping.Such a phenomena may result in objectionable, cold down-drafts on theoccupants of the room.

Therefore, in order to provide an air distribution apparatus whichmaintains the air flow between some acceptable maximum and minimumvalues, air flow regulators are employed which automatically regulatethe volume flow of air from the air supply means to the terminaldiffuser ports. Such regulators in order to provide maximum efficiencyand optimum service must be responsive not only to pressuredifferentials within the air distribution apparatus itself, but theymust also be responsive to changes in the ambient temperature within theenclosed area. Accordingly, air flow distribution systems typicallyemploy a thermostat disposed within the enclosed area which generates asignal in response to the ambient temperature therein. This signal istransmitted to the volume flow regulator which adjusts the air flow tothe terminal port in response thereto. Thus, the air distribution systemis self-adjusting so as to maintain the temperature within the enclosurewithin acceptable limits.

Pneumatic thermostats have been suggested for use in such airdistribution systems. These temperature responsive devices generate froma substantially constant pressure air supply a pressurized air signalindicative of ambient temperature. When the system employs a moresophisticated volume flow regulator, it is sometimes desirable that thethermostat be able to reference its output signal not only totemperature but also to the pressure in the system downstream from theregulator. An air distribution apparatus requiring such a thermostat isdescribed in U.S. Pat. application Ser. No. 416,202. However, in orderto reference the output signal of the thermostat totally to the pressuredownstream of the regulator, it is required that the thermometricelement be sealed from the ambient air. This, in turn, makes accuratesensing of the ambient temperature more difficult.

Moreover, in order to generate a pressurized air signal which isindicative of ambient temperature the pneumatic thermostat must beprovided with a substantially constant pressure air supply. Prior artdevices typically employ a central air supply which feeds all thepneumatic thermostats of the air distribution system. Such anarrangement is not only costly, but it also renders the operation of theindividual flow regulators dependent upon the central air supply to itsthermostat. Thus, the individual air flow regulators are not completelyindependent.

Therefore, according to the present invention, there is provided apneumatic thermostat for use in conjunction with an air distributionsystem which is capable of generating a pressurized air signalreferenced not only to ambient temperature but also to the pressure inthe distribution system downstream from the air flow regulator.Moreover, the pneumatic thermostat of the present invention uses as itsair supply source the air flow within the air distribution systemitself. Thus, the need for a central air supply for each individualthermostat is completely eliminated.

SUMMARY OF THE INVENTION

The present invention is directed toward an improved pneumaticthermostat which is capable of reducing a variable pressure air supplyto a substantially constant pressure air flow and generating from thisconstant pressure air flow an air pressure signal which is indicative ofthe ambient temperature.

The improved thermostat is comprised, generally, of means for receivinga variable pressure air supply; means for generating from the air supplya substantially constant pressure air flow; a chamber having inlet meansfor receiving said air flow; temperature responsive means for adjustingthe pressure within the chamber in response to changes in ambienttemperature; outlet means communicating with said chamber fortransmitting a pressure signal indicative of said temperature; and,means for aspirating ambient air by and through said temperatureresponsive means.

Thus, the improved thermostat may be comprised of a pressure reducingchamber, a thermometric chamber containing a temperature sensing device,and an aspirator. More specifically, means for receiving the variablepressure air supply communicates with a means for separating the airsupply into two portions. The pressure reducing chamber includes a lowersection adapted to receive the first portion of the air supply, an uppersection in communication with an air outlet port, and means forintermittently bleeding the lower section to the upper section in orderto maintain a constant pressure within the lower section. The lowersection is also provided with a restriction nozzle which is adapted tocontinuously bleed from this lower section to the pressure transmittingchamber a substantially constant pressure air flow. The pressuretransmitting chamber has an exhaust nozzle which vents to thethermometric chamber, the thermometric chamber also having an ambientair inlet port and an air outlet port. Within the thermometric chamberthere is disposed means for variably inhibiting the air flow from theexhaust nozzle, automatically, in response to changes in ambienttemperature, thereby producing a pressure within the pressuretransmitting chamber which is indicative of the ambient temperature. Athird outlet port is provided which is in communication with thepressure transmitting chamber and is adapted to transmit a pressuresignal which is also indicative of ambient temperature. Finally, a meansfor aspirating the thermostatic chambr is positioned adjacent to thesecond air outlet port. This aspirating means is in communication withthe air supply receiving means and it is adapted to utilize the secondportion of the air supply to aspirate the ambient air through thethermometric chamber.

The improved pneumatic thermostat of the present invention is ideallysuited for use in conjunction with an air flow regulator in an airdistribution system wherein it is desired to provide a constant volumeair flow to the terminal ports of the system. Moreover, the air flow isadjustable in response to both pressure variations within thedistribution system itself and the ambient temperature within theenclosed area to be serviced by the system.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood by reference to the drawings.

FIG. 1 is a side elevational view of one embodiment of the pneumaticthermostat of the present invention.

FIG. 2 is also a side elevational view showing an alternative embodimentof the pneumatic thermostat of the present invention.

FIG. 3 is a schematic representation of an air distribution system whichemploys a thermostat of the present invention.

FIG. 4 is a perspective view showing a modular embodiment of thepneumatic thermostat of the present invention.

FIG. 5 is a sectional view taken along line 5--5 of FIG. 4 showing ingreater detail the pressure reducing and pressure transmitting chambersof the modular embodiment.

FIG. 6 is a sectional view taken along line 6--6 of FIG. 4 showing ingreater detail the thermometric chamber and the aspirator of the modularembodiment.

FIG. 7 is a sectional view taken along line 7--7 of FIG. 4.

FIG. 8 is a sectional view taken along line 8--8 of FIG. 4.

FIG. 9 is a schematic representation of an air distribution system whichemploys the modular thermostat of the present invention.

FIGS. 10 and 11 are perspective views of another alternative embodimentof the pneumatic thermostat of the present invention shown in a typicalceiling mounted installation.

FIG. 12 is a sectional view taken along line 12--12 of FIG. 10.

DETAILED DESCRIPTION OF THE INVENTION

One embodiment of the improved pneumatic thermostat of the presentinvention is illustrated in FIG. 1, and it is shown as typically mountedin the ceiling of the enclosure which it services. The thermostat,designated generally as 20 includes means for receiving an air supply atvariable pressure P₁. The air supply receiving means, as for example airinlet port 22, communicates with conduit 24 and orifice 26 in order toseparate the air supply into two portions. A first portion of the airsupply passes through conduit 24 and air restriction 28 to the pressurereducing chamber 30. The second portion of the air supply passes throughorifice 26. Chamber 30 is comprised of a lower section 31 and an uppersection 32 which includes an air outlet port 34. Disposed within chamber30 and between the lower and upper sections, 31 and 32 respectively, isseat 36 which has an aperture therein defining an air flow passageway.Also disposed within upper section 32 of the pressure reducing chamber30 is a ball 38 which, by force of gravity, removably engages the seat36 so as to intermittently close the air flow passageway. Finally, thelower section 31 of chamber 30 includes a restriction nozzle 39 whichcontinuously bleeds a substantially constant air flow to a pressuretransmitting chamber 40. Chamber 40, in turn, communicates with anexhaust nozzle 42 which vents chamber 40 into a thermometric chamber 50.

Disposed within the thermometric chamber 50 is a thermometric element,which includes a bi-metallic lever 53 fixedly secured to an adjustmentlever 54 both of which are pivotally mounted at pivot 55: A flapper 56is also mounted on pivot 55, and it is positioned adjacent to the nozzle42 so as to inhibit the flow of air therefrom. Fixedly secured to theextremity of flapper 56 is a linking member 59 which is adapted toengage bi-metallic lever 53 as the lever moves upwardly in response to achange in ambient temperature. An extension spring 58 may be employed tobias flapper 56 and linking element 59 toward nozzle 42.

Thus, in a manner well known in the art, the bi-metallic lever 53 willengage the linking member 59 and, in response to temperature changes,thereby vary the distance separating the nozzle 42 from the flapper 56.This action, in turn, will vary the air discharge from nozzle 42 and inthis way the pressure within the pressure transmitting chamber 40 isregulated so as to correspond to, or be indicative of, ambienttemperature.

Chamber 40 also communicates with an air outlet conduit 44 and outletport 46 through which a pressurized air signal P_(c) may be transmitted.This signal, of course, would also be indicative of ambient temperature.

The thermometric element of the present invention further includes anextension spring 57 which biases adjusting lever 54 against adjustingrod 60. A set point knob 62 is secured to adjusting rod 60 so as toprovide a means for setting an initial pressure signal P_(c) in responseto a given temperature.

The thermometric chamber 50 further includes an ambient air inlet port64 and an outlet port 66. Positioned adjacent to outlet port 66 isconduit 68 and orifice 26. Conduit 68 communicates with outlet port 66via air flow passageway 69 such that as the second portion of the airsupply passes through orifice 26 and into conduit 68, a venturi-likesuction is applied to the port 66. Accordingly, ambient air is drawninto chamber 50 via port 64 and out through outlet port 66 andpassageway 69, as is shown by the arrows. In this way ambient air iscontinually aspirated through the thermometric chamber 50 so thatthermometric element adjusts in response to the true ambienttemperature.

It may also be desirable to filter the portion of the air supplyutilized to generate the pressure signal P_(c) in order to insure thatforeign matter does not accumulate in the various nozzles within thethermostat. Such accumulations could adversely affect the accurateoperation of the device. Accordingly, a filtering element 70 may beemployed and positioned within conduit 24 so as to remove dirt particlesfrom the air supply. The filter may be composed of felt, plastic,cellulose, or other suitable materials. However, it should besufficiently porous so as to avoid any significant reduction in thepressure P₁ which might adversely affect the pressure stabilizationproduced in the lower section 31 of chamber 30.

A threaded port 72 may be provided in the wall of the pressuretransmitting chamber 40 through which a tap could be made to determineP_(c) for servicing and adjustment. Of course, the port is sealablyclosed by the tap screw 74 and o-ring 76 when the device is inoperation.

Another embodiment of the improved thermostat of the present invention,making use of an alternative bi-metallic lever and flapper arrangement,is illustrated in FIG. 2. In this embodiment a flapper 56' is fixedlysecured to the bi-metallic lever 53' adjacent to pivot 55, at a baseportion of the lever which is immobile in response to changingtemperature. Flapper 56' extends beyond the free end of bi-metalliclever 53', as is shown in FIG. 2, and is positioned adjacent to theexhaust nozzle 42' so as to inhibit the flow of air therefrom. A spring68' may also be employed so as to bias flapper 56' toward nozzle 42'.

The operation of this embodiment is identical to that of the arrangementshown in FIG. 1, such that a pressure signal P_(c) is generated andtransmitted from outlet port 46 which is indicative of the ambienttemperature as sensed in chamber 50.

The improved thermostat of the present invention as illustrated in theembodiments set forth above operates suitably in conjunction with apneumatic-activated air flow regulator in an air distribution system,such as is shown schematically in FIG. 3. An airflow A, provided by apressurized air source 11, flows through an air flow regulator 12 to theterminal port diffuser 14 from which it is discharged into the enclosureserviced by the system. In order that the regulator 12 be responsive tochanges in ambient temperature, it is adapted to adjust to a pressurizedair signal P_(c) generated by the thermostat 20 and conveyed to theregulator via conduit 16.

So as to make the regulator 12 and thermostat 20 independent of anyexternal energy source, the thermostat 20 utilizes as its air supply aportion of the air flow A taken from the system upstream of theregulator 12. This air supply, at a variable pressure P₁, is conveyed tothe air inlet port 22 of the thermostat 20 via conduit 17. In order togenerate a pressure signal indicative of ambient temperature this airsupply at pressure P₁, which may vary in magnitude through a range of5:1 or more, must be reduced to a substantially constant pressure airflow. Thus, a portion of the air supply flows through the filter 70 andinto the lower section 31 of the pressure reducing chamber 30 which isseparated from upper section 32 by the ball 38 resting in the seat 36.Of course, the resulting reduced pressure P_(r) which will be maintainedin the lower section 31 will be dependent upon the weight of the ball38, the pressure P₂ in the upper section 32 and the size of thecontinuous bleed air restriction 39. The ball 38 is of such a weightthat its downward force equals the area of the aperture in seat 36multiplied by the desired reduced pressure P_(r) which drives the airflow through the restriction 39 and into the pressure transmittingchamber 40.

As has been noted above, it is sometimes desirable that the pressuresignal P_(c) generated by the thermostat 20 will be at least partiallyreferenced to the pressure within the air distribution system downstreamof the regulator. Accordingly, the outlet port 34 of upper section 32communicates with air flow A downstream of regulator 12 via conduit 18.This arrangement insures that the air flow through the pressure reducingchamber 30 will always be from the lower section 31 to the upper section32, since P₁ must always be greater than P₂.

Therefore, air at pressure P₁ flows into lower section 31 until thepressure is slightly above P_(r) + P₂. At this point the ball 38 willlift from the seat 36 and air will bleed from section 31 to section 32until the pressure in section 31 is slightly below P_(r) + P₂. At thispoint the ball 38 will again engage seat 36 and the air flow passagewaywill be closed. Thus, this arrangement will intermittently bleed lowersection 31 so as to provide a substantially constant reduced pressureP_(r), referenced to P₂, for a wide variation in air supply pressure P₁.

In this manner, a constant pressure is supplied to the pressuretransmitting chamber 40 via restriction nozzle 39. This chamber, inturn, vents to the thermometric chamber 50 via exhaust nozzle 42, andthe discharge from nozzle 42 is regulated by the position of flapper 56and bi-metallic lever 53. Thus, the resulting pressure P_(c) within thepressure transmitting chamber 40 will be indicative of ambienttemperature and the given initial set point made with adjusting rod 60and set knob 62. This pressure may be transmitted via conduit 44 andoutlet port 46 to conduit 16 and the regulator 12.

A further embodiment of the present invention is illustrated in FIGS. 4to 9. In this embodiment modular components are utilized with thepressure reducing and pressure transmitting chambers physicallyseparated from the thermometric chamber and the aspirator. As can beseen in FIGS. 4 and 5, the pressure reducing and pressure transmittingchambers, 130 and 140 respectively, are combined into a single unit,designated generally as 110, which is preferably mounted on a wall 120of the duct work of the air distribution system. The unit 110 is mountedover a porous, low pressure drop filter 170 which also serves, at itscompressed perimeter, as a gasket to prevent air flow leakage from thesystem. Air at a pressure P₁ flows through the filter 170 and airrestriction 114 into the lower section 131 of the pressure reducingchamber 130. The lower section 131, like the previous embodimentsdescribed hereinabove, bleeds intermittently into the upper chamber 132via a ball and seat arrangement. Upper section 132 also communicates viaoutlet port 134 and a conduit 118 with the air distribution systemdownstream from the regulator at a pressure P₂. Thus, a reduced pressureP_(r) is maintained substantially constant within section 131, whichpressure drives the air through air restriction 139 and into thepressure transmitting chamber 140.

The thermometric chamber 150 along with the means 160 for aspiratingthis chamber are, in this embodiment, separated from the unit 110 andmounted at a remote location within the enclosure serviced by the airvolume regulator.

The air nozzle 142 is provided an air supply via conduit B whichcommunicates with the outlet 141 for the pressure transmitting chamber140. Of course, the pressure within chamber 140 will be regulated so asto correspond to ambient temperature in the same manner as is describedfor the embodiments described above. Accordingly, a pressure signalP_(c) indicative of ambient temperature will be transmitted via outlet146 and conduit 116 directly to the volume flow regulator.

The aspirating means 160, as is shown in FIGS. 4 and 7, is provided anair supply via conduit C which communicates with the air distributionsystem, as is shown in FIG. 8, through the port 161 in the unit 110.Thus, the air supplied to the aspirator is filtered by filtering means170 and no individual filtering element need be provided.

It will be apparent that the operation of the modular thermostatdescribed above is substantially the same as that of the integratedembodiments previously discussed.

As can be seen in FIG. 9, an airflow A, provided by a pressurized airsource 11, flows through an air flow regulator 12 to the terminal portdiffuser 14 from which it is discharged into the enclosure serviced bythe system. In order that the regulator 12 be responsive to changes inambient temperature, it is adapted to adjust to a pressurized air signalP_(c) generated by the modular thermostat of the present invention andconveyed to the regulator via conduit 116.

So as to make the regulator 12 and thermostat independent of anyexternal energy source, the unit 110 utilizes as its air supply aportion of the air flow A taken from the system upstream of theregulator 12. This air supply, at a variable pressure P₁, enters theunit 110 at the air inlet port 122. In order to generate a pressuresignal indicative of ambient temperature this air supply at pressure P₁,which may vary in magnitude through a range of 5:1 or more, must bereduced to a substantially constant pressure air flow. Thus, a portionof the air supply flows through the filter 170 and into the lowersection 131 of the pressure reducing chamber 130 which is separated fromupper section 132 by the ball 138 resting in the seat 136. Of course,the resulting reduced pressure P_(r) which will be maintained in thelower section 131 will be dependent upon the weight of the ball 138, thepressure P₂ in the upper section 132 and the size of the continuousbleed air restriction 139. The ball 138 is of such a weight that itsdownward force equals the area of the aperture in seat 136 multiplied bythe desired reduced pressure P_(r) which drives the air flow through therestriction 139 and into the pressure transmitting chamber 140.

As has been noted above, it is sometimes desirable that the pressuresignal P_(c) generated by the thermostat be at least partiallyreferenced to the pressure within the air distribution system downstreamof the regulator. Accordingly, the outlet port 134 of upper section 132communicates with air flow A downstream of regulator 12 via conduit 118.This arrangement insures that the air flow through the pressure reducingchamber 130 will always be from the lower section 131 to the uppersection 132, since P₁ must always be greater than P₂.

Therefore, air at pressure P₁ flows into lower section 31 until thepressure is slightly above P_(r) + P₂. At this point the ball 138 willlift from the seat 136 and air will bleed from section 131 to section132 until the pressure in section 131 is slightly below P_(r) + P₂. Atthis point the ball 38 will again engage seat 136 and the air flowpassageway will be closed. Thus, this arrangement will intermittentlybleed lower section 131 so as to provide a substantially constantreduced pressure P_(r), referenced to P₂, for a wide variation in airsupply pressure P₁.

In this manner, a constant pressure is supplied to the pressuretransmitting chamber 140 via restriction nozzle 139. This chamber, inturn, vents to the thermometric chamber 150 via conduit B and theexhaust nozzle 142, and the air discharge from nozzle 142 is regulatedby the position of flapper 156 and bimetallic lever 153. Thus, theresulting pressure P_(c) within the pressure transmitting chamber 140will be indicative of ambient temperature and the given initial setpoint made with adjusting rod 160 and set point knob 162. This pressuremay be transmitted via outlet port 146 and conduit 116 to the regulator12.

One principle advantage of this modular embodiment of the presentinvention is the need for only two air flow conduit lines, A and B, fromthe air distribution system to the remotely placed thermometric chamberand aspirator. It will be recognized that three such conduits arerequired when the embodiments shown in FIGS. 1 and 2 are stationedremote from the regulator and air distribution system. Thus, greaterease in installation, maintenance and repair is effected with themodular device. Moreover, separate servicing of the unit 110 or thethermometric chamber 150 and aspirator 160 may be performed. Finally,manufacture of the improved thermostat is simplified through the use ofmodular components.

Still another embodiment of the present invention is illustrated inFIGS. 10-12. This embodiment is directed toward a modified modularthermostat which assures accurate sensing of ambient temperature withinthe room or enclosure serviced by the air distribution system.

Due to the high cost of labor incurred in the installation of heating,cooling and ventillating systems, it is preferred to pre-assemble theheat sensing and aspirating component of the modular thermostat with theterminal diffuser of the air distribution system. In this manner boththe diffuser and the temperature sensing device may be installedsimultaneously thereby reducing labor costs.

Referring now to FIG. 10, a typical assembly is shown with the heatsensing and aspirating component 200 mounted at one end of a terminaldiffuser 202. This assembly may be conveniently positioned in theceiling 204 of the enclosure and is engaged with a discharge duct 206 ofthe air distribution system.

It has been discovered, however, that when the heat sensing andaspirating component disclosed hereinabove is used in such an assembly,accurate temperature control is difficult to attain. This difficulty isattributed to the fact that conditioned air discharged through diffuser202 will heat or cool the metal support structure 210. This structure,through conduction and radiation, changes the temperature of the airspace 212. For example, cooled air discharged through diffuser 202 mayhave a temperature as low as 50° F. This cool air may lower thetemperature in chamber 212 to about 65° F which, in turn, may result ina "reading" by the thermosensing apparatus which is lower than theambient temperature of the room being serviced by the air distributionsystem.

Accordingly, the improved thermostat of the present invention mayinclude means for aspirating the area adjacent to the thermometricchamber 250 in order to insure that the thermosensing apparatus is notaffected be conductive or radiant heat transfer. A preferred mode forperforming this "external" aspiration is illustrated in FIGS. 11 and 12wherein a second aperture 252 is disposed in the bottom of theaspirating tube 262 downstream from the primary aspirating aperturewhich services the thermometric chamber 250. This arrangement allows theaspirating means 260 to draw ambient air through the air space 212, asindicated by the arrows in FIG. 12, thereby eliminating the conductiveand radiant heat transfer potential which might adversely affect theaccuracy of the thermostat.

This dual aspiration embodiment is constructed, installed, and operatedin substantially the same manner as is the modular component embodimentdescribed hereinabove. Thus, the aspirating means 260 is provided an airsupply via conduit C which communicates with the air distributionsystem, and the air nozzle (not shown) is provided its air supply viaconduit B which communicates with the pressure reducing component of thethermostat. Room air is thereby drawn through both the thermometricchamber 250 and the air space 212 assuring accurate temperature sensingwhich, in turn, controls the bleed through the thermostat's air nozzle.In this manner an air pressure signal may be generated which isindicative of the true ambient temperature in the enclosure serviced bythe air distribution system.

It can be seen from the foregoing, that the improved thermostat of thepresent invention provides a pressurized air signal indicative ofambient temperature, which signal is generated from a variable pressureair supply and which may be used to activate an air flow regulatorwithin an air distribution system. Moreover, where the regulator sorequires, the pressure signal may be referenced at least partially tothe pressure downstream from the regulator. Finally, the thermostatutilizes no external source of energy other than the derived from theair flow within the air distribution system, so that each air regulatorand its respective thermostat operate as an independent unit.

Of course, it should be understood that the preferred embodiments of theimproved pneumatic thermostat, herein disclosed, may be modified withoutdeparting from the spirit and scope of the invention and withoutdiminishing its attendant advantages.

I claim:
 1. In an air flow distribution apparatus having a means forsupplying pressurized air, a means for diffusing said air into anenclosed area, and a means for regulating the air flow to said diffusingmeans from said supply means in response to an air pressure signalindicative of temperature within the enclosed area, the improvementcomprising: a pneumatic thermostat capable of generating from a variablepressure air supply said air pressure signal indicative of ambienttemperature, said thermostat including a pressure reducing chamberhaving a lower and an upper section; said lower section adapted toreceive from said air flow distribution apparatus upstream from saidregulating means said variable pressure air supply and said uppersection having a first outlet port in communication with the air flowdistribution apparatus downstream from said regulating means; means forintermittently bleeding said lower section to said upper section toproduce a constant pressure within said lower section; a restrictionnozzle adapted to continuously bleed from said lower section to apressure transmitting chamber a substantially constant pressure airflow, said pressure transmitting chamber communicating with an exhaustnozzle which vents to a thermometric chamber, said thermometric chamberhaving an inlet port to receive ambient air from the enclosed area and asecond outlet port; means disposed within said thermometric chamber andadjacent said exhaust nozzle for variably inhibiting the air flow fromsaid exhaust nozzle automatically in response to changes in ambienttemperature thereby producing a pressure within said pressuretransmitting chamber indicative of said ambient temperature, a third airoutlet port in communication with said pressure transmitting chamber tothereby transmit said pressure signal to said regulating means; andmeans for aspirating said thermometric chamber disposed adjacent to saidsecond air outlet port, said aspirating means in communication with saidvariable pressure air supply and adapted to utilize said air supply toaspirate ambient air through said thermometric chamber.
 2. The improvedair flow distribution apparatus of claim 1 wherein said pressurereducing chamber and said pressure transmitting chamber are positionedadjacent to said regulating means, said thermometric chamber and saidaspirating means are positioned remote from said regulating means, andconduit means connect said pressure transmitting chamber with saidexhaust nozzle and said aspirating means with said variable pressure airsupply.
 3. The improved air flow distribution apparatus of claim 2wherein filtering means are disposed between said variable pressure airsupply and both said air receiving means and said aspirating means. 4.In an air flow distribution apparatus having a means for supplyingpressurized air, a means for diffusing said air into an enclosed area,and a means for regulating the air flow to said diffusing means fromsaid supply means in response to an air pressure signal indicative oftemperature within the enclosed area, the improvement comprising: apneumatic thermostat including means for receiving a variable pressureair supply; means for generating from said air supply said pressuresignal indicative of said temperature, said signal being referenced tothe pressure in said air distribution apparatus downstream from saidregulating means; and means for aspirating ambient air by and throughsaid temperature responsive means.
 5. The improved air flow distributionapparatus of claim 4 wherein said signal generating means includes apressure reducing chamber in communication with said air receivingmeans, said chamber having an air outlet in communication with the airdistribution apparatus downstream from said regulating means and an airrestriction nozzle, and means for intermittently bleeding said chamberthrough said outlet to produce a constant pressure within said chamber.6. In an air flow distribution apparatus having a means for supplyingpressurized air, a means for diffusing said air into an enclosed area,and a means for regulating the air flow to said diffusing means fromsaid supply means in response to an air pressure signal indicative oftemperature within the enclosed area, the improvement comprising: apneumatic thermostat capable of generating from a variable pressure airsupply said air pressure signal indicative of ambient temperature, saidthermostat including means for receiving from said air flow distributionapparatus upstream from said regulating means said variable pressure airsupply, said receiving means in communication with means for separatingsaid air supply into two portions, a pressure reducing chamber having alower and an upper section, said lower section adapted to receive thefirst portion of said air supply, said upper section having a firstoutlet port in communication with said air distribution apparatusdownstream from said regulating means, means for intermittently bleedingsaid lower section to said upper section to produce a constant pressurewithin said lower section, a restriction nozzle adapted to continuouslybleed from said lower section to a pressure transmitting chamber asubstantially constant pressure air flow, said pressure transmittingchamber communicating with an exhaust nozzle which vents to athermometric chamber, said thermometric chamber having an inlet port toreceive ambient air from the enclosed area and a second outlet port,means disposed within said thermometric chamber and adjacent saidexhaust nozzle for variably inhibiting the air flow from said exhaustnozzle automatically in reponse to changes in ambient temperaturethereby producing a pressure within said pressure transmitting chamberindicative of said ambient temperature, a third air outlet port incommunication with said pressure transmitting chamber to therebytransmit said pressure signal to said regulating means, said signal alsobeing indicative of ambient temperature, and means for aspirating saidthermometric chamber disposed adjacent to said second air outlet port,said aspirating means in communication with said air supply receivingmeans and adapted to utilize the second portion of said air supply toaspirate ambient air through said thermometric chamber.
 7. In an airflow distribution apparatus having a means for supplying pressurizedair, a means for diffusing said air into an enclosed area, and a meansfor regulating the air flow to said diffusing means from said supplymeans in response to an air pressure signal indicative of temperaturewithin the enclosed area, the improvement comprising: a pneumaticthermostat capable of generating from a variable pressure air supplysaid air pressure signal indicative of ambient temperature, saidthermostat including means for receiving from said air flow distributionapparatus upstream from said regulating means said variable pressure airsupply, a pressure reducing chamber having a lower and an upper section,said lower section adapted to receive said air supply from said airreceiving means, said upper section having a first outlet port, meansfor intermittently bleeding said lower secton to said upper section toproduce a constant pressure within said lower section, a restrictionnozzle adapted to continuously bleed from said lower section to apressure transmitting chamber a substantially constant pressure airflow, said pressure transmitting chamber communicating with an exhaustnozzle which vents to a thermometric chamber, said thermometric chamberhaving an inlet port to receive ambient air from the enclosed area and asecond outlet port, means disposed within said thermometric chamber andadjacent said exhaust nozzle for variably inhibiting the air flow fromsaid exhaust nozzle automatically in response to changes in ambienttemperature thereby producing a pressure within said pressuretransmitting chamber indicative of said ambient temperature, a third airoutlet port in communication with said pressure transmitting chamber tothereby transmit said pressure signal to said regulating means, saidsignal also being indicative of ambient temperature, and means foraspirating said thermometric chamber disposed adjacent to said secondair outlet port, said aspirating means in communication with saidvariable pressure air supply and adapted to utilize said air supply toaspirate ambient air through said thermometric chamber.